The present invention is directed toward radiation sensors and, more particularly, to a novel method for improving the hysteresis and excitation after-glow performance of a radiation-responsive sensor by electron irradiation of the radiation-converting phosphor used therein.
Sensors for detecting radiation flux, such as the x-ray flux detectors used in computed tomography systems, are known to the art. Such sensors may consist of a bar of a conversion material, such as thallium-doped cesium iodide (CsI:Tl), which acts to convert x-ray flux to optical photons, and a photon detector positioned adjacent to the bar of conversion material, for converting the optical photons into an electric current, which may be amplified and subsequently processed to determine the x-ray flux incident upon the conversion material bar of the radiation sensor. The phosphor utilized in such a scintillation detection system has been found to be subject to both (a) a hysteresis effect, i.e. a reversible change in the optical photon output of the scintillation phosphor, with time and under constant radiation excitation, and (b) the presence of a phosphorescent tail, or after-glow, from the phosphor after the cessation of impingent radiation convertible to optical photons. These phenomena result in errors between consecutive measurements of incident radiation flux in scintillation detector systems, especially when the incident radiation flux undergoes a change from a relatively large incident flux magnitude to a relatively small incident flux magnitude. In radiation detection systems, such as computed tomography systems, where a high degree of accuracy is required, these errors have proven to be extremely undesirable. Accordingly, a method for reducing the hysteresis and after-glow phosphorescence tail of the scintillation phosphor member utilized in a radiation detector, is highly desirable.